The described technology relates generally to systems for switching the frequency of electrical power provided by portable power modules and, more particularly, to systems for switching the frequency of electrical power provided by portable power modules trailerable over public roads and capable of providing at least approximately one megawatt of electrical power.
There are many occasions when temporary electrical power may be required. Common examples include entertainment and special events at large venues. As the demand for energy quickly outstrips supply, however, temporary electrical power is being used in a number of less common applications. For example, as electrical outages occur with increasing regularity, many commercial enterprises are also turning to temporary electrical power to meet their demands during peak usage periods.
A number of prior art approaches have been developed to meet the rising demand for temporary electrical power. One such approach is a mobile system that generates electrical power using a liquid fuel motor, such as a diesel fuel motor, drivably coupled to an electrical generator. This system is capable of producing up to two megawatts of electrical power and can be housed within a standard shipping container, such as a standard 40-foot ISO (International Standard Organization) shipping container. Enclosure within a standard shipping container enables this system to be quickly deployed to remote job sites using a conventional transport vehicle, such as a typical tractor truck.
Temporary electrical power systems that use liquid fuels, such as petroleum-based fuels, however, have a number of drawbacks. One drawback is associated with the motor exhaust, which may include undesirable effluents. Another drawback is associated with the expense of procuring and storing the necessary quantities of liquid fuel. As a result of these drawbacks, attempts have been made to develop temporary electrical power systems that use gaseous fuels, such as natural gas.
One such attempt at a gaseous fuel system is illustrated in FIG. 1, which shows a side elevational view of a power generation system 100 in its normal operating configuration. The power generation system 100 includes a motor 110 drivably coupled to a generator 120. The motor 110 is configured to burn a gaseous fuel, such as natural gas, and is capable of mechanically driving the generator 120 to produce an electrical power output on the order of one megawatt. The motor 110 and generator 120 are housed within a standard 40 foot ISO shipping container 102, which is supported by a trailer 103 having a tandem axle rear wheel-set 104. The trailer 103 can be coupled to a typical transport vehicle, such as a tractor truck, for movement of the container 102 between job sites.
Unlike their diesel fuel powered counterparts, gaseous fuel power generation systems of the prior art, such as that shown in FIG. 1, have an exhaust gas silencer 114 and a motor coolant radiator 118 installed on top of the container 102 during normal operation. This configuration is dictated by a number of factors, including the size of the gaseous fuel motor 110 and the amount of heat it gives off during operation. The size of the motor 110 reduces the space available inside the container 102 for the exhaust gas silencer 114 and the radiator 118, and the large amount of heat generated by the motor creates an unfavorable thermal environment inside the container for the radiator. Although the exhaust gas silencer 114 and the radiator 118 are installed on top of the container 102 during normal operation, during movement between job sites these components are removed from the top of the container to facilitate travel over public roads.
Electrical equipment in different parts of the world often use different frequencies of electrical power. For example, electrical equipment in Europe is generally configured to use 50 Hz power while electrical equipment in the United States is generally configured to use 60 Hz power. The prior art power generation system 100 can be provided in one of two configurations depending on the frequency of electrical power output desired. In the 50 Hz configuration, the motor 110 is connected directly to the generator 120 with a coupling so that the generator turns at the same number of revolutions per minute (RPM) as the motor. In this configuration, the motor 110 and the generator 120 may both turn at 1500 RPM to produce electrical power at 50 Hz. In the 60 Hz configuration, however, a gearbox is interconnected between the motor 110 and the gearbox 120 to step up the generator RPMs relative to the motor. In this configuration, the motor 110 may turn at 1500 RPM and the generator 120 may turn at 1800 RPM to produce electrical power at 60 Hz.
A number of shortcomings are associated with the method for changing the frequency of electrical power provided by the power generation system 100. For example, if the power generation system 100 is configured for use in Europe, then it will not have a gearbox installed between the motor 110 and the generator 120 and the motor and generator will both operate at 1500 RPM to produce power at 50 Hz. However, if it is later desired to use this power generation system in the United States, then a gearbox will have to be installed between the motor 110 and the generator 120 so that the generator will operate at 1800 RPM and produce power at 60 Hz when the motor is operating at 1500 RPM. If still later this power generation system is returned to Europe, the gearbox will accordingly have to be removed. Removing and installing this gearbox depending on where the power generation system 100 is located is a time-consuming process that adds to the initial expense of procuring the gearbox.
Additional shortcomings are associated with the prior art power generation system 100. One shortcoming is the number of transport vehicles required to deploy the power generation system 100 to a given job site. For example, although the container 102 with the motor 110 and the generator 120 inside can be transported to the job site using only one transport vehicle, an additional transport vehicle is also required to carry the exhaust gas silencer 114 and the radiator 118. In addition, once at the job site, both the exhaust gas silencer 114 and the radiator 118 need to be installed on top of the container 102 and the necessary structural and functional interfaces connected and verified. The exhaust gas silencer 114 and the radiator 118 must then be removed from the top of the container 102 when it comes time to move the power generation system 100 to a second job site.
The foregoing shortcomings of the prior art power generation system 100 offset many of the benefits associated with such a system. Therefore, a temporary electrical power generation system that uses gaseous fuel and has the ability to provide at least approximately one megawatt of electrical power without these shortcomings would be desirable.